While PET (polyethylene terephthalate) is widely accepted as the
material of choice for plastic beverage containers, various
complications inherent in the stretch-blowmolding process have always
presented seemingly insurmountable problems to bottle manufacturers.
Chief among them, according to Johnson Controls, Manchester, MI, has
been the detrimental effect of corrosion on the metal molds, along with
pitting, wear, and other problems associated with corrosion.

Most of the mold assemblies used at Johnson Controls combine both
stainless steel (not hardened) and aluminum (a notoriously
"soft" metal in their construction. Moisture condensation
during the manufacturing process is one source of corrosive attack on
both metals. Galvanic reaction at the interface where both metals meet
is another. Both usually result in pitting of the precise, polished mold
surfaces--highly detrimental to maintaining clarity in the finished
container.

In addition, extensive wear, from the constant abrasion between the
plastic and the metal mold sections during the molding cycle aggravated
pitting problems. This led to frequent mold repolishing, significantly
shortened mold life, increased labor costs, and costly quality-control
monitoring. Added to that, the release of the finished container from
the mold cavity was severely impeded.

Johnson Controls has solved the problem by using "synergistic
coatings" originally developed for solving similar difficulties
that had been encountered in the use of both steel and aluminum in the
US space program. Created in a multistep process by General Magnaplate
Corp, Linden, NJ, synergistic coatings are not coatings in the
conventional sense of the word. The process combines the advantages of
anodizing or hard-coat metal finishing with the controlled infusion of
low-friction polymers and/or dry lubricants.

In the Nedox[reg] process, nickel is first electrodeposited on the
metal surface. This deposit contains countless micro-pores which are
enlarged in a series of proprietary treatments. Next, the surface is
sealed with a controlled infusion of sub-micron size particles of
selected polymers. It is then given a final heat treatment which ensures
the mechanical cross-linking of the polymer particles to the substrate.

The synergistic coating gives the steel part permanent non-stick
lubricity along with improved surface hardness, better abrasion
resistance, and exceptional protection against corrosion and chemical
attack.

Unlike conventional coatings, the Nedox impregnation cannot chip,
peel, or be rubbed off. Important to the avoidance of equipment
hang-ups, very few solid substances will permanently adhere to the
polymer-impregnated surface of the coated part.

A second General Magnaplate process, tradenamed Tufram[reg], solved
the wear problems on the mold's aluminum sections by making the
component's soft aluminum surfaces as hard as the surface of steel.

In its first step, the oxide crystals expand and form a porous
surface layer. Upon the introduction of sub-micron polymers into the
newly formed surface, the polymer particles interlock with the oxidized surface, forming a continuous lubricating polymer-ceramic surface that
will not chip, peel, or delaminate.

The result is an aluminum surface which ASTM standard Taber
abrasion tests show to have greater abrasion resistance than
case-hardened steel or hard-chromium plating.

PHOTO : In the Nedox[reg] coating process, sub-micron, low-friction
polymers are infused into enlarged pores of porous nickel plated on
steel, copper, or aluminum surface and then heat treated for increased
hardness and controlled thickness.

PHOTO : In the Tufram[reg] process, a permanent synergistic surface
is created on aluminum by mechanical crosslinking of polymers and
oxidized aluminum crystals: 1. surface growth, 2. original metal
surface, 3. penetration of metal.

COPYRIGHT 1991 Nelson Publishing
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